The present invention relates to the field of electronic test systems. More specifically, in one embodiment the invention provides an improved method and device for performing tests on semiconductor wafers, such methods otherwise known as wafer test via probing.
Various types of wafer test and probe equipment are well known to those of skill in the art, and are broadly used in semiconductor manufacturing operations. Such equipment is used to provide electrical signals to a semiconductor die, generally formed on a wafer, and monitor the response of the die to the electrical signals. Wafer test and probe equipment is made by a variety of manufacturers including, for example, Electroglas, KLA, Teradyne, Schlumberger, and Trillium.
The tests are normally conducted prior to dicing the wafer and chip packaging. The wafer is placed on a prober chuck, indexed, and each die is tested. The testing operation normally involves placing a probe card with a number of probe tips in contact with the die at selected locations (for example, the bond pads). Predetermined voltage patterns are then applied to the die, and the response of the die to the signals is monitored. If the die exhibits an appropriate response, the die is assumed to be "good." Otherwise the die is rejected, or appropriate remedial actions are taken. Such tests are performed on a wide variety of semiconductor products ranging from DRAMs and SRAMs to microprocessors and the like.
As semiconductor devices operate faster, it has become necessary to adopt "overhead" test techniques. In this technique, a section of the tester referred to as the test head is positioned on the top plate of the prober and then docked. Lines of signal transmission are, therefore, kept very short, avoiding cross-talk at high frequencies. Using these techniques involves the use of a printed circuit board with a plurality of pins extending downwardly therefrom. While meeting with substantial success, such prior systems have also exhibited certain difficulties. For example, electrical contact to the die is often made via delicate metallic pins extending from the PCB or probe card. The arrangement of the pins on the probe card, and the circuitry on the probe card varies from application to application. For example, the arrangement of pins on a 1M DRAM will be radically different than the arrangement of pins on a 4M DRAM, and the arrangement of both of the pins on a DRAM will obviously vary radically from the arrangement of pins on a microprocessor.
Therefore, when it is desired to switch test equipment from one product to another, it is necessary to remove the probe card and replace the probe card with a different probe card. This has often been a time consuming and difficult task for a number of reasons. For example, in many systems the probe card is mounted under a test head, which must be undocked before the probe card may be removed. This is often difficult because most test heads weigh between 250 and 750 pounds. Further, the interface between the test head and the probe card must be disassembled and reassembled. Still further, recalibration is required after replacement of a probe card.
Further, the probe cards often require maintenance after repeated contacts with semiconductor wafers, particularly due to damage to the contact pins on the probe cards. Conventionally, those of skill in the art have had no effective way of recording the operating history of a probe card. Therefore, contact failures are detected using, for example, the methods such as the ones disclosed in U.S. Pat. No. 5,019,771 and the card is replaced or repaired after a failure occurs. Since the problem is corrected when it arises, this procedure often results in undesirable down time.
It becomes particularly difficult to maintain records on individual probe cards when the probe cards are frequently moved into and out of a probe system due to, for example, changes in the products which are tested by the system. In such operations it becomes necessary to manually label the various probe cards, and manually enter information regarding probe card usage on data sheets or into a computer. This often becomes difficult or impractical when a large number of cards are in use, and is susceptible to human error.
From the above it is seen that an improved system and method for conducting wafer probe tests is needed.